The invention relates to a telescopic feed beam for a rock drill, the feed beam comprising a lower beam and an upper beam arranged on top of each other and parallel with each other in the longitudinal direction, whereby the rock drill is arranged to be installed movably in the upper beam in its longitudinal direction and a transfer cylinder is arranged to act between the upper beam and the lower beam to move the upper and the lower beam with respect to each other in the longitudinal direction.
Rock drilling devices are frequently used in various drilling situations. Thus it is sometimes necessary to drill short holes in confined spaces and longer holes when space permits. This cannot be done by using conventional feed beams, for which reason different drilling devices are normally used for various purposes. Sometimes it is, however, necessary to use the same drilling device for drilling holes in different conditions. For this purpose, various telescopic beams have been developed where the feed beam is formed by two feed beam sections that move with respect to each other in the longitudinal direction, i.e. an upper beam, along which the rock drill moves, and a lower beam. In this case, the upper beam and the lower beam are typically coupled by means of slide rails and slide pads to move with respect to each other in the longitudinal direction. When drilling takes place in confined spaces, the feed beam sections are arranged to overlap to as great an extent as possible to achieve as short a total length as possible. On the other hand, when longer holes are drilled, the feed beam sections are moved with respect to each other to achieve as long a feed beam as possible. In that case, longer drill rods are naturally employed in the drilling. As the drillings proceeds, the drill rod penetrates into rock, in which case the length of the feed beam is first shortened typically by moving the farther feed beam section in the drilling direction. After this feed beam section has moved onto the top of the other feed beam section so that the feed beam is at its shortest, the rock drill is moved along the feed beam section to allow the utilization of the whole drill rod length. A pressure medium operated transfer cylinder is rather commonly used to provide the movement between the feed beams, the cylinder being coupled between the feed beam sections so that when the piston of the transfer cylinder is moved with respect to the cylinder, the feed beam sections move with respect to each other. Such a solution is known from Finnish patent no. 97253, for instance.
Prior art feed beam solutions involve various practical problems; for example, it is difficult to carry out servicing because of the confined space available in the feed beams. Furthermore, if the transfer cylinder is installed in the space between the feed beam sections to protect it from dirt and mechanical stress and the feed beam is installed at the end of the boom of a rock drilling device, it may not be that easy to service and, if necessary, to repair or replace the transfer cylinder. Nowadays, in particular, more attention is paid to the quickness and ease of service to minimize losses in the productive time of a rock drilling device. It is thus necessary to find new solutions for achieving this.